A wide variety of polymeric materials have been utilized as electrical insulating materials for power cables and other electrical devices. Ethylene propylene co-polymers and ethylene, propylene and diene terpolymers (EPDM) having polyethylene-type crystallinity are commercially used in medium voltage electrical insulation compounds. These compounds are applied as an insulation member over either a metallic conductor or a semi-conductive substrate in a multi-step extrusion process. Typical insulating compounds may also include fillers and various additives.
EPDM polymers can provide good insulating properties. However, surface characteristics of the extrudate in a compound based on these elastomeric polymers may not be smooth at typical high extrusion rates, which is desirable because of improved interfacial adhesion between the cable layers. Therefore, one prior method attempted to reduce the extrusion rates, but it was not economically advantageous. The present disclosure provides a way to decrease the surface roughness, thereby increasing the smoothness, while maintaining high extrusion rates.
It would be desirable to have a polymeric composition suitable for use in compounds for electrical applications, such as cable coating compounds, which exhibit decreased surface roughness, improved tack and adhesion, enhanced physical properties and/or performance, and provide improved manufacturing capability and quality, without loss of tensile strength or elongation at break.